Testing apparatus for carrier systems



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March 23, 1954 l. MoLNAR TESTING APPARATUS FOR CARRIER SYSTEMS l2 Sheets-Sheet 1l Original Filed July l0, 194'? INVENTOR. IMRE `MOLNAH March 23, 1954 l. MOLNAR TESTING APPARATUS EoR CARRIER SYSTEMS 12 Sheets-Sheet l2 Original Filed July 10, 194'.

ALARM SENDER 680 R686 ST INVENTOR. [MRE MOL/VAR TTYS AC SOURCE Patented Mar. 23, 1954 TESTING APPARATUS FDR CARRIER SYSTEMS Imre Molnar, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Original application July 10, 1947, Serial No.

760,136. Divided and this application March 30, 1951, Serial No. 218,389

12 claims. l

The present invention relates to telephone systems and more particularly to such systems of the intertoll dialing type employing carrier links. This application is a division of the copending application of Imre Molnar, Serial No. 760,136, filed July 10, 1947, now Patent No. 2,603,717, granted July l5, 1952.

It is a general object of the invention to provide an intertoll dialing system involving a net- More particularly, Figs. 2 and 3 illustrate diagrammatically the automatic switching apparatus and one of the pieces of carrier equipment disposed in the remote exchange l0, as well as the details of one of the trunk circuits disposed therein; Figs. 4, 5 and 6 illustrate diagrammatically the automatic switching apparatus and one of the pieces of carrier equipment disposed in the tandem exchange 20, as well as the details of work of automatic exchanges and offices, protwo diierent trunk circuits disposed therein; Fig. vided with subscriber substations, paystations, 6 also illustrates diagrammatically one of the manual dial switchboards and automatic dial pieces of carrier current equipment disposed at switchboards, whereby the usual trunk and toll the way station 30, as well as the details of one connections may be set up and supervised emof the trunk circuits and one of the alarm senders ploying the carrier links. disposed thereat; Fig. 7 illustrates diagrammati- Another object of the invention is to provide in cally one of the pieces of carrier equipment disa telephone system including a remote exchange posed at the main ofce 40, as well as thedetails of the automatic type, a tandem exchange of the of one of the trunk circuits, one of the alarm reautomatic type, and a main oflice provided with ceivers, and one of the cord circuits disposed a switchboard, an improved arrangement for settherein; Fig. 8 illustrates diagrammatically the ting up connections involving the stations in the automatic switching apparatus and one of the exchanges and the switchboard in the office. pieces of carrier equipment disposed in the main A further object of the invention is to provide oce 40, as well as the details of a different one of in a telephone system including an exchange conthe trunk circuits disposed therein; Figs. 9 and 10 nected to an unattended way station and an illustrate diagrammatically the automatic switchoflice connected to the way station by a carrier ing apparatus and one of the pieces of carrier link, an improved arrangement for automatically equipment disposed in the distant oiiice 50, as Checking the Operating condition of the carrier well as the details of one of the trunk circuits link and fOr Operating a Signal in the oflice in the disposed therein; Fig. 11 illustrates diagramevent of a faulty condition of the carrier link. matically the elements incorporated in the carrier Further features 0f the IlVentiOn pertain t0 3U equipment provided at the way station 30; and the Dartiular arrangement 0f the Circuit ele- Fig. 12 illustrates diagrammatically the elements ments 0f the SYStem, whereby the above-Outlined incorporated in the alarm sender provided at the and additional operating features thereof are way Station 3.0, attained.

The invention, both as to its organization and The automatw telephone system method of operation, together with further ob- Referring now more particularly to Fig. 1, the jects and advantages thereof, will best be underautomatic telephone system there illustrated stood by reference to the following specication comprises the remote exchange I0 serving a numtaken in connection with the accompanying ber of ordinary subscriber substations, including drawings in which Figure 1 is a diagrammatic 40 the subscriber substation TH, and a number of illustration of an automatic telephone system einpaystations, including the paystation TI2. The bodying the present invention and comprising a subscriber substation TII is provided with a subremote exchange l0, a tandem exchange 20, a scriber line 2li extending thereto and having a way station 30, a main ofce and a distant line circuit 213 individually associated therewith; oflice Figs. 2 to 10, inclusive, taken together, 45 and the paystation TI2 is provided with a line illustrate the details of the apparatus incorpo- 212 extending thereto and having a line circuit rated in the automatic telephone system illus- 2M individually associated therewith. Also the trated in Fig. 1 and embodying the features of remote exchange l0 comprises a plurality of the invention as briefly outlined above; Fig. 11 groups of finder-selector links, the i'lrst group illustrates the carrier equipment provided at the 50 including the finder-selector link 203 and proway station 30; and Fig. 12 illustrates the alarm vided with a distributor 204; as well as a plurality sender provided at the way station 30. Figs. 2 of groups of local connectors, the lrst group of to 10, inclusive, should be arranged from left to local connectors including the local connector right in end-to-end relation in order to form a 205. Preferably, the subscriber line 2li extendunified diagram. 56 ing to the subscriber substation TII and the line 2 l2 extending to the paystation T|2 are arranged 1n the first group of lines and are accordingly accessible both to the finders of the rst group of finder-selector links 203, etc., and to the rst group of local connectors 205, etc. Further, the remote exchange I comprises a group of incoming selectors, including the incoming selector 206, having access to the diierent groups of local connectors; the local connector 205 in the rst group being accessible to the incoming selector 206 via the trunk 20-1 extending thereto.

The remote exchange l0 and the tandem exchange 20 are interconnected by a plurality of channels of carrier equipment; the first channel illustrated including the line 60 extending between the remote exchange l0 and the tandem exchange 20 and respectively terminating in the carrier equipment 394 provided in the remote exchange l0 and in the carrier equipment 494 provided in the tandem exchange 20. The carrier equipment 394 is connected to a trunk circuit 200 individual thereto provided in the remote exchange I0; which trunk circuit 200 is connected by a trunk 230 to the incoming selector 206 individual thereto. Also the trunk circuit 200 comprises two additional trunks 220 and 225; both accessible to the selectors of the different groups of finder-selector links. Finally, the selectors of the dierent groups of finder-selector links in the remote exchange I0 also have access to the different groups of local connectors therein. Specifically, the selector of the finder-selector link 203 has access to the local connector 205 via the trunk 201 extending thereto.

The tandem exchange 20 serves a number of ordinary subscriber substations, including the subscriber substation T2I, and a number of paystations, including the paystation T22. The subscriber substation T2| is provided with a subscriber line 42| extending thereto and having a line circuit 423 individually associated therewith; and the paystation T22 is provided with a line 422 extending thereto and having a line circuit 424 individually associated therewith. Also the tandem exchange 20 comprises a plurality of groups of finder-selector links, the first group including the finder-selector link 426 and provided With a distributor 425; as well as a plurality of groups of local connectors, the rst group of local connectors including the local connector 421. Preferably, the subscriber line 42| extending to the subscriber substation T2| and the line 422 extending to the paystation T22 and arranged in the rst group of lines and are accordingly accessible both to the finders of the rst group of finder-selector links 426, etc., and to the rst group of local connectors 421, etc. Further, the tandem exchange 20 comprises a rst group of incoming selectors, including the incoming selector 429, having access to the different groups of local connectors; and a second group of incoming selectors, including the incoming selector 434, having access to the different groups of local connectors; the local connector 421 in the rst group being accessible to the incoming selectors 429, etc., and 434, etc., via the trunk 428 extending thereto. The carrier equipment 494 in the tandem exchange 20 is connected to a trunk circuit 400 individual thereto; which trunk circuit 400 is connected by a trunk 435 to the incoming selector 429 individual thereto. Also the trunk circuit 400 comprises an additional trunk 430 accessible to the selectors of the different groups of finder-selector links and to the group of incoming selectors 434, etc.

The tandem exchange 20 and the way station 30 are interconnected by a group of trunk lines, including the trunk line 665. Each of the trunk lines terminates in a trunk circuit provided in the tandem exchange 20 and in a trunk circuit provided at the Way station 30; the trunk line 665 terminating in the trunk circuits 500 and 600 respectively provided in the tandem exchange 20 and at the way station 30. The trunk circuit 500 is connected by a trunk 520 to the incoming selector 434 individual thereto. Also the trunk circuit 500 comprises two additional trunks 5|0 and 5|5 respectively accessible to the selectors of the different groups of finder-selector links and to the incoming selectors 429, etc. Finally, the selectors of the different groups of finderselector links in the tandem exchange 20 also have access to the diierent groups of local connectors therein. Specifically, the selector of the finder-selector link 426 has access to the local connector 421 via the trunk 428 extending thereto.

The way station 30 and the main oflce 40 are interconnected by a plurality of channels of carrier equipment; the first channel illustrated including the line 10 extending between the way station 30 and the main office 40 and respectively terminating in the carrier equipment 649 provided at the way station 30 and in the carrier equipment 194 provided in the main ofllce 40. The carrier equipment 694 is connected to the trunk circuit 600 individual thereto at the way station 30; which trunk circuit terminates one end of the trunk line 665 extending between the tandem exchange 20 and the way station 30, as

. previously noted. Also a plurality of alarm senders 680, etc. are provided at the way station 30 and respectively connected to the carrier equipment 694, etc., thereat.

The carrier equipment 194 provided in the main oice 40 is connected to a trunk circuit 100 individual thereto; which trunk circuit terminates in a jack J appearing before an operator switchboard in the main oice 40; which operator switchboard 165 comprises a plurality of cord circuits, including the cord circuit 166. Also a plurality of alarm receivers 110, etc., are provided in the main oice 40 and respectively connected to the carrier equipment 194, etc.

The main oiice 40 serves a number of ordinary subscriber substations including the subscriber substation T4I. The subscriber substation T4| is provided with a subscriber line 84| extending thereto and having a line circuit 842 individually associated therewith. Also the main oilice 40 comprises a local switch train 844 provided with a distributor 843. The subscriber line 84| extending to the subscriber substation T4| has access to and is accessible to the local switch train 844. Also the main oilice 40 comprises a group of C. L. R. trunks including the C. L. R. trunk 846. The C. L. R. trunk 846 is accessible to the local switch train 844 via a trunk 845 extending thereto and is also provided with a trunk 841 extending therefrom which terminates in a jack J848 appearing before the operator switchboard 165. Moreover the main oii'ice 40 comprises a toll switch train 805 having access to the lines 84|, etc.. respectively extending to the subscriber substations T4I, etc.; which toll switch train 805 has a trunk 806 extending thereto and terminating in a jack J 801 appearing before the operator switchboard 165. Further, the main oilce 40 comprises a group of incoming selectors, including the incoming selector 8|2, having access to the toll switch train 805 via the trunk 806 extending thereto. Also the main ofiice 40 comprises a group of toll trunks inward 809, etc. The toll trunk inward 809 is accessible to the incoming selector 8|2 via the trunk 808 extending thereto and is provided with a. trunk 8 I 0 extending therefrom and terminating in a jack J8|| appearing before the operator switchboard 165.

The main office 40 and the distant ofce 50 are interconnected by a plurality of channels of carrier equipment, the rst channel illustrated including the line 80 extending between the main office 40 and the distant ofce 50 and respectively terminating in the carrier equipment 894 provi-ded in the main oce 40 and in the carrier equipment 994 provided in the distant office 50. The carrier equipment 894 is connected to a trunk circuit 800 individual thereto in the main oflice 40; which trunk circuit 800 is connected by a trunk 815 to the incoming selector 8|2 individual thereto. Also the trunk circuit 800 terminates in a jack J 8|5 appearing before the operator switchboard 165.

The distant oiiice 50 serves a number of ordinary subscriber substations, including the subscriber substation T5I. The subscriber substation T5I is provided with a subscriber line |05| extending thereto and having a line circuit |052 individually associated therewith. Also the distant oilice 50 comprises a local switch train |054 provided with a distributor |053. The subscriber line |05| extending to the subscriber substation T5I has access to and is accessible to the local switch train |054. Also the distant oce 50 comprises a Strowger dial toll board |060 provided with a plurality of toll operator positions, one of which is indicated at |06I. Each toll operator position isprovided with a group of nder-selector links individual thereto; the group of finderselector links individual to the toll operator position I 06| including the nder-selector link |062. Further, the distant oice 50 comprises a group of C. L. R. trunks, including the C. L. R. trunk |056; the C. L. R. trunk |056 is accessible to the local switch train |054 via a trunk |055 extending thereto; which C. L. R. trunk circuit |056 is also provided with a trunk |051 extending therefrom that is accessible to the finders of the nder-selector links associated with the various toll operator positions at the 4Strowger dial toll board |060. Moreover, the distant omce 50 comprises a toll switch train |038 having access to the lines |05|, etc., respectively extending to the subscribersubstations T5I, etc.; which toll switch train |038 has a trunk |031 extending thereto that is accessible to the selectors of the nder-selector links associated with the various toll operator positions at the Strowger dial toll board |060. Further, the distant oflice 50 comprises a group of incoming selectors, including the incoming selector |036, having access to the toll switch train |038 via the trunk |031 extending thereto. Also the distant office 50 comprises a group of toll trunks inward |066, etc. The toll trunks inward |066 are accessible to the incoming selector |036 via a trunk |065 extending thereto and is provided with a trunk |061 extending therefrom and accessible to the finders of the nder-selector links associated with the various toll operator positions at the Strowger dial toll board |060.

A carrier equipment 994 provided in the distant omce 50 is connected to the trunk circuit 900 individual thereto; which trunk circuit 900 is con- |036 individual thereto. Also the trunk circuit 900 is provided with a trunk 040 incoming thereto that is accessible to the selectors of the nderselector links associated with the various toll earator positions at the Strowger dial toll board The apparatus incorporated in the automatic telephone system Preferably, the carrier system interconnecting the remote exchange |0 and the tandem exchange 20, the carrier system interconnecting the way station 30 and the main oce 40 and the carrier system interconnecting the main office 40 and the distant oce 50 are identical and each comprises a type 32 Lenkurt unit of the character disclosed in the copending application of Imre Molnar, Serial No. 728,422, filed February 14, 1947, now Patent No. 2,559,l65granted July 3, 1951. Alternatively, the carrier equipment interconnecting the various exchanges, ofllces and way stations. mentioned may be of the radio-link type disclosed in the copending application of Imre Molnar, Serial No. 746,929, filed May 9, 1947, now Patent No. 2,525,914, granted September 26. 1950. Thus the carrier equipment 494, 194 and 994 respectively disposed at the east termini of the lines 60, 10 and 80, and respectively comprising portions of the first channels in the three carrier current systems mentioned, transmit at a carrier frequency of 15.95 kc. for signalling purposes, transmit the lower side band of the carrier frequency 15.95 kc. (13.1 to 15.7 kc.) for communication purposes, receive a carrier frequency of 24.55 kc. for signalling purposes, and receive the lower side band of the carrier frequency 24.55 kc. (21.7 to 24.3 kc.) for communication purposes. Similarly, the carrier equipment 394, 694 and 894 respectively disposed at the West termini of the lines 60, 10 and 80, and respectively comprising portions of the first channels in the three carrier current systems mentioned, transmit at a carrier frequency of 24.55 kc. for signalling purposes, transmit the lower side band of the carrier frequency 24.55 kc. (21.7 to 24.3 kc.) for communication purposes, receive a carrier frequency of 15.95 kc. for signalling purposes, and receive the lower side band of the carrier frequency 15.95 kc. (13.1 to 15.7 kc.) for ycommunication purposes.

Also, each carrier equipment 394, etc., comprises an outgoing signal transmitting channel including a rst carrier frequency oscillator and a transmitting amplifier provided with a plate circuit controlled by an associated signal-out relay; as well as an outgoing communication channel including a balanced modulator connected to the first carrier frequency oscillator and an associated transmitting band pass filter. Also, each carrier equipment mentioned comprises an incoming signal channel including a rectifier and a signal-in relay; as Well as an incoming communication channel including a balanced demodulator connected to a second carrier frequency oscillator and an associated receiving band pass filter. Also each carrier equipment mentioned comprises a transmitting direction lter connected to the associated outgoing signal transmitting channel and to the associated outgoing communication channel; as well as a re- 'ceiving direction filter connected to the associated incoming signal channel and to the associated incoming communication channel. Further, each carrier equipment mentioned comprises a high pass line filter connected between the associated line terminus and the transmitting direction filter and the receiving direction filter. Finally, each line tei-minus is connected by a low pass filter to other voice frequency equipment. This conventional equipment described above and disclosed in the previously mentioned copending Molnar application, permits utilization of the lines 60, 10 and 80 in other voice frequency equipment in a manner well under stood.

Specifically, as illustrated in Fig. 11, the carrier equipment 694 provided at the way station 30 comprises a high pass line filter |H3 directly connected to the west portion of the line 10, a receiving direction lter I I I4, and a transmitting direction filter HI5, both connected to the high pass line iilter HI3, a receiving line amplier ||I6 connected to the receiving direction filter HI4, and a transmitting line amplifier I I I1 connected to the transmitting direction lter IH5. The high pass line filter I I3 is arranged to pass high frequency carrier signals in the overall range 6.5 to 28.45 kc., and to block the passage of audio frequency signals in order to prevent interference with the carrier system. The receiving direction filter II|4 is arranged to pass carrier frequency signals toward the lower end of the overall carrier frequency range, and particularly the carrier frequencies between 6.5 and 15.95 kc., and to block carrier frequency signals toward the upper end of the overall carrier frequency range, and particularly the carrier frequencies between 18.0 and 28.45 kc. On the other hand, the transmitting direction filter I I I5 is ai'- ranged to pass carrier frequency signals toward the upper end of the overall carrier frequency range, and particularly the carrier fequencies between 18.0 and 28.45 kc., and to block carrier frequency signals toward the lower end of the overall carrier frequency range, and particularly the carrier frequencies between 6.5 and 15.95 kc.

Further the carrier equipment 694 comprises a receiving communication channel including a receiving band pass filter |I2I connected to the receiving line amplifier ||I6 and arranged to pass the lower side band of the carrier frequency 15.95 kc. (13.1 to 15.7 kc.), an attenuation equalizer H22 connected to the receiving band pass filter I|2I, a gain control H23 connected to the attenuation equalizer H22, and a demodulator H24 connected to the gain control H23. Further, a carrier frequency oscillator H28 having an output frequency of 15.95 kc. is connected by an oscillator pad H21 to the demodulator H24; and the demodulator H24 is connected to a receiving low pass filter H25 ari ranged to pass audio frequency signals; which, in turn, is connected by a receiving amplifier I |26 to a hybrid coil H30 provided with a balancing network II3I. Further, the hybrid coil H30 is connected to the line conductors 60| and 602.

Further the carrier equipment 694 comprises a signal receiving ilter ||5I connected to the receiving line amplifier I||6 and arranged to pass the carrier frequency 15.95 kc.; which, in turn, is connected by way of a receiving amplifier H52 to a rectifier H53. The output of the rectifier |53 is connected by way of a signal bias control II 54 to a D. C. amplifier I |55, the output of which is connected to the signal-in relay R695. The D. C. amplier H55 normally supplies sufficientcurrent to the winding of the signal-in relay R695 to maintain the latter relay in its operated position, whereby the operated signal-in relay R695 maintains completed, at the contacts 666, the path for applying battery potential to the signal-in conductor C504. However, when the receiving signal channel receives the carrier frequency 15.95 kc., the rectifier H53 is controlled by the receiving amplier H52 to produce a current that is supplied to the signal bias control H54, whereby the bias applied to the D. C. amplifier H55 is increased in order to cause the output current thereof to be reduced suiciently to bring about the restoration of the signal-in relay R695. Upon restoring the signal-in relay R695 interrupts, at the contacts 696, the previously-mentioned path for applying battery potential to the signal-in conductor C604. Accordingly, as signal pulses of 15.95 kc. carrier frequency are received by the receiving signal channel, the signal-in relay R695 follows, repeating at the contacts 696, corresponding battery impulses over the signal-in conductor C604.

Further, the carrier equipment 694 comprises a transmitting communication channel, includ ing a transmission low pass filter ||4I connected to the hybrid coil H30 and arranged to pass audio frequencies; which, in turn, is connected by way of an input pad I |42 to a modulator I |43. A carrier frequency oscillator H48 having an output frequency of 24.55 kc. is connected by an oscillator pad H41 to the modulator H43; and the modulator H43 is connected by an output pad H44 to an attenuation equalizer H45. The attenuation equalizer I |45 is connected to a transmission band pass filter I |46, arranged to pass the lower side band of the carrier frequency 24.55 kc. (21.7 to 24.3 kc.) and to block the upper side band of the carrier frequency 24.55 kc.; which, in turn, is connected to the transmission line amplifier I||1.

Further the carrier equipment 694 comprises a transmission signal channel including the no1'- mally restored signal-out relay R691 connected to the signal-out conductor 603; which signalout relay R691 is adapted to be operated in order to close its contacts 696 included in the plate circuit of a transmission amplifier H63; which, in turn, is connected to the carrier frequency oscillator H48 by way of the oscillator pad H41. Also the transmission amplifier |63 is connected by way of a signal transmission pad H64 to a signal transmission filter |65 arranged to transmit the carrier frequency 24.55 kc. Finally, the signal transmission filter H65 is connected to the transmission line amplier |H1. Accordingly, as the signal-out relay R691 is controlled over the signal-out conductor C603, it is operated and then restored; whereby the signal-out relay R691 completes, and then interrupts, at the contacts 698, the plate circuit extending to the transmission amplifier H63; whereby corresponding pulses of 24.55 kc. carrier frequency are transmitted from the transmission amplifier H63 via the signal transmission pad H 64 and thence through the signal transmission lter H65 into the transmission line amplifier I||1.

In view of the foregoing description of the connection and arrangement and the mode of operation of the carrier equipment 694 provided at the way station 30, the arrangement of the carrier equipment 194, etc., in the central oice 40, etc., will be apparent.

As shown in Fig. 2, preferably each of the finder-selector links 203, etc., each of the local connectors 205, etc., and each of the incoming selectors 206, etc., are of the conventional Strowger types; while the distributor 204 and the line circuits 2|3, 2I4, etc., are of any suitable types. Finally, each of the subscriber substations TII, etc., is provided with conventional substation apparatus; each subscriber line 2||,

etc., is provided with a meter, not shown, individual thereto; and each of the paystations T|2, etc., is of the character of that disclosed in Fig. 3 of United States Patent No. 2,137,409, granted November 22, 1938, to Talbot G. Martin and Clarence E. Lomax. Specically, a paystation of this type comprises, among other elements, a transmitter bridged by an asymmetrical current conducting device in the form of a copper oxide rectifier; whereby a person at the paystation may control the extension of a connec tion therefrom and converse with an operator without depositing a coin thereat. Also, the person at the paystation can normally extend a connection therefrom to a subscriber substation, but cannot talk to the subscriber thereat until a coin has been deposited at the paystation, as a consequence of the blocking action of the copper oxide rectifier with respect to the transmitter when the polarity of the line is reversed in a local connection.

Preferably, each of the trunk circuits in the remote exchange I is identical to the trunk circuit 200 that comprises, as shown in Figs. 2 and 3, a relay group including a timer relay R235, a reverse battery relay R240, a series relay R250, a switch relay R260, a supervisory relay R210, a timer relay R280, an answer relay R3l0, a dial relay R320, a line relay R330, a hold relay R340, a signal-in relay R350, two digit relays R360 and R310, a hold relay R380 and a tone relay R390. Also, the trunk circuit 200 comprises an impedance 251 and a busy tone transformer 346. At this point it is noted that the trunk circuit 200 is connected to the carrier equipment 394 by a pair of line conductors C30| and C302, a signal-out conductor C303 and a signal-in conductor C304; and that the apparatus provided in the carrier equipment 394, as previously explained, comprises a signal-in relay R395 and a signal-out relay R391.

In the tandem exchange 20, as shown in Fig. 4, each of the finder-selector links 426, etc., each of the local connectors 421, etc., and each of the incoming selectors 429, etc., and 434, etc., are of the conventional Strowger types; while the distributor 425 and the line circuits 423, 424, etc., are of any suitably types. Finally, each of the subscriber substations T2 etc., is provided with conventional substation apparatus; each of the subscriber lines 42|, etc., is provided with a meter, not shown, individual thereto; and each of the paystations T22, etc., is of the character of that disclosed in Fig. 3 of the previously mentioned Martin et al. patent.

In the tandem exchange 20, preferably each of the trunk circuits in the group, including the trunk circuit 400, is identical thereto; which trunk circuit 400 comprises, as shown in Fig. 4, a relay group including a supervisory relay R440, an answer relay R445, a signal-in relay R450, a dial relay R455, a switch relay R460, a line relay R410, a hold relay R480, a control relay R490, and a hold relay R400, as well as an impedance 458. At this point it is noted that the trunk circuit 400 is connected to the carrier equipment 494 by a. pair of line conductors C40| and C402, a signalout conductor C403 and a signal-in conductor C404; and that the apparatus provided in the carrier equipment 494, as previously explained, comprises a signal-in relay R495 and a signal-out relay R491.

Also. in the tandem exchange 20, preferably.

each oi' the trunk circuits in the group, including the trunk circuit 500, is identical thereto; which trunk circuit 500 comprises, as shown in Figs. 5 and 6, a relay group including a reverse battery relay R530, two timer relays R540 and R550, a supervisory relay R560, a tone relay R565, a hold relay R510, a supervisory relay R530, a seize relay R585, a control relay R590, an answer relay R595, a line relay R6|0, a pulse relay R620, a switch relay R630, and a dial relay R640. Also. the trunk circuit 500 comprises an ordinary battery indicated, a booster battery 6|6 and arepeating coil RC650.

Preferably, each of the trunk circuits at the way station 30 is identical to the trunk circuit 600 that comprises, as shown in Fig. 6, a relay group including a signal-out relay R660, and a signal-in relay R610. Also, the trunk circuit 600 comprises two asymmetrical current conducting devices 666 and 661, in the form of copper oxide rectiflers, and a repeating coil RC615. At this point it is noted that the trunk circuit 600 is connected to the carrier equipment 694 by a pair oi line conductors C60| and C602, a signal-out conductor C603 and a signal-in conductor C604; and that the apparatus provided in the carrier equipment 694, as previously explained, comprises a signal-in relay R695 and a signal-out relay R691.

Preferably, in the way station 30, each of the alarm senders is identical to the alarm sender 680 which comprises, as shown in Fig. 6, a motor 68| operative from a commercial source of single phase A. C. power and operatively associated with a set of switch springs S682 and with a gearbox 683. The gearbox 683 is adapted to time operation of the motor 68| and at the expiration of ten minutes to open the associated contacts S684 and to close the associated contacts S685. Further, the alarm sender 680 comprises a start relay R686.

The alarm sender 680 provided at the way station 30 may be of any well-known type, but is preferably of the type disclosed in U. S. Patent No. 2,425,620, granted on August l2, 1947, to Leslie A. Kempton. Specifically. as shown in Fig. l2, the alarm sender 680 comprises a timer motor 68| of a well-known type including a field element |20| carrying a plurality of poles |202 provided with windings |203 and cooperating shading coils |204, as well as a rotatable armature |205 carried by an operating shaft |206 mounted for both rotation and longitudinal sliding movements. The timer motor 68| is mounted in the vertical direction, and the operating shaft |206 carries a drive gear |201 that normally disengages an associated driven gear |208 forming a part of the gear train 683. However, when the windings |203 of the timer motor 68| are ener-v gized, the field ux lifts the armature |205 from its normal lower position into its upper position so as to engage the drive gear |201 with the driven gear |208 in an obvious manner. Subsequently when the windings |203 are deenergized, the weight of the armature |205 causes it to be returned to its lower position disengaging the drive gear |201 and the driven gear |208.

Further the alarm sender 680 comprises a series of reduction gears, including the driven gear |209, in the gear train 683; which driven gear |209 is fixed on the lower end of a camshaft |2|0 mounted for rotation and carrying an operating cam I2 I. The operating cam |2|| cooperates with upper and lower cam followers |2|2 and I2 I3; and the upper end of the camshaft |2|0 has one end of a spirally wound ribbon spring |2|4 fixed thereto, the other end of the spring |2|4 being xed to an exterior support. The spring |2|4 biases the camshaft |2| 0 in the counterclockwise direction, as viewed from the top thereof into a normal position wherein a stop |2|5 xed to the camshaft l2 l0 engages an exteriorly mounted stop |2|6. In the normal position of the camshaft |2|0, the cam follower |2|3 rides into a. notch I 2| 1 provided in the lower surface of the cam |2|| so as to operate the set of switch springs S682 into its closed position. On the other hand, the cam follower |2|2 disengages a projection |2|8 provided on the upper surface of the cam |2|| so that the cam follower |2|2 is operated to close the set of switch springs S684 and to open the set of switch springs S685. Finally the alarm sender 680 comprises the start relay R686 that is governed by the signal-in relay R610 and the signal-out relay R660, and that governs the signal-out conductor C603, as well as a control switch |2|9.

Considering now the operation of the alarm sender 680 and assuming that the signal-in relay R610 occupies its operated position and the signal-out relay R660 occupies its restored position, a circuit, including the contacts 614 and 664 and the sets of switch springs S682 and S684, is completed for operating the start relay R686. Upon operating, the start relay R686 completes, at its contacts 681, a holding circuit, including the set of switch springs S684, for energizing the winding thereof; and completes, at the contacts 688, a circuit for energizing the windings |203 of the timer motor 68|, further assuming that the control switch |2|8 has just been closed. When the windings |203' of the timer motor 68| are thus energized, the armature |205 is lifted from its lower position into its upper position and rotated at the synchronous speed established by the A. C. source of current supply, the timer motor 68| being of the shaded pole synchronous type, whereby the drive gear |201 engages the driven gear |208 effecting rotation of the driven gear |209 in the gear train 683 so that the camshaft |2|0 is rotated at the timed rate in the clockwise direction, as viewed from the upper end thereof. As the camshaft |2|0 is rotated out of its normal position, the stop |2|5 moves away from the stop |2|6, and the cam |2|| rides the cam follower |2|3 out of the notch |2|1 so as to interrupt the pick-up circuit for the start relay R686; whereby, at this time, the start relay R686 is retained operated only via its holding circuit, including the contacts 614, 664 and 681 and the set of switch springs S684. Operation of the timer motor 68| continues and ultimately upon the expiration of ten minutes the projection 2 8 is rotated around and under the cam follower |2 2 so that the set of switch springs S684 is opened and the set of switch springs S685 is closed. Opening of the set of'switch springs S684 interrupts the holding circuit for retaining operated the start relay R686, whereby the latter relay restores shortly thereafter, it being of the slow-torelease type. Closing of the set of switch springs S685 applies ground potential via the contacts 681, 664, and 614 to the signal-out conductor C603.

After the expiration of a short time interval, the start relay R686 restores interrupting, at the contacts 681, a further point in the holding circuit for energizing the winding thereof, as well as a point in the previously traced path for applying ground potential to the signal-out conductor C603, whereby the ground potential mentioned is applied to the signal-out conductor C603 Only during the short time interval or restoration time of the start relay R686. Also upon restoring the start relay R686 interrupts, at the contacts 688. the circuit for energizing the windings |203 of the start motor 68| so that the armature |205 is returned to its normal lower position causing the drive gear' |201 to disengage the driven gear |208. At this time, the energy that was stored in the spring |2|4 is released, whereby the cam |2|| is rotated in the counterclockwise direction, as viewed from the top of the camshaft |2|0, from its limit position back into its normal position, the normal position being re-established by the cooperation between the stops |2 I5 and |2|6. When the cam |2|| is thus moved out of its limit position, the cam follower |2|2 disengages the projection I2 I8 so that the set of switch springs S685 is opened and the set of switch springs S684 is closed. When the cam |2|| is returned back into its normal position, the cam follower |2|3 again engages the notch |2|1 closing the set of switch springs S682. When the sets of switch springs S682 and S684 are thus reclosed, the pickup circuit for the start relay R686 is again completed so that another cycle of operation of the timer motor 68| may be initiated in the manner described above. Accordingly, the alarm sender 680 is operative cyclically to transmit a pulse of ground potential for a short time interval over the signal-out conductor C603 each ten minute interval of time, as long as the signal-in relay R610 is retained in its operated position and the signal-out relay R660 is retained in its restored position.

In view of the above description of the alarm sender 680 provided at the way station 30, it is believed that the mode of operation of the alarm receiver provided in the main oice 40 will be apparent.

In the main oice 40, preferably each of the trunk circuits in the group, including the trunk circuit 100, is identical thereto; which trunk circuit 100, as shown in Fig. 7, terminates in the jack J before the operator switchboard 165, as previously noted, and comprises a relay group including a signal-in relay R105, a jack relay R1 0, and a sleeve relay R120. Also, the trunk circuit 100 comprises a busy lamp L132 and a line lamp L133 disposed at the operator switchboard 165. At this point it is noted that the trunk circuit 100 is connected to the carrier equipment 194 by a pair of line conductors C10| and C102, a signalout conductor C103 and a signal-in conductor C104; and that the apparatus provided in the carrier equipment 194, as previously explained, comprises a signal-in relay R195 and a signal-out relay R191.

' Preferably, each of the cord circuits disposed at the operator switchboard 165 is identical to the cord circuit 166 which, as shown in Fig. '1, terminates into front and rear plugs P148 and P158, respectively, and comprises a dial D160, a dial key K131, a ring key K136, a talk front key K134 and a talk rear key K135. Also, the cord circuit 166 comprises a front supervisory lamp L141, a rear supervisory lamp L151 and a relay group including a dial front relay R140, a supervisory front relay R145, a dial rear relay R and a supervisory rear relay R155. Finally, it is noted that the Lcord circuit 166 is associated with a headset 161 disposed at the operator switchboard 165 and with an interrupted generator 138.

Preferably, in the main office 40, each of the alarm receivers is identical to the alarm receiver 110 which comprises, as shown in Fig. 7. a motor aevaaac 113 operative from a commercial source of single phase A. C. power and operatively associated with two sets of switch springs S111 and S118 and with a gearbox 114. The gearbox 114 is adapted to time operation of the motor 113 and at the expiration of 91/2 minutes to close the associated contacts S115 and at the expiration of 10i/g minutes to close the associated contacts S116. Further, the alarm receiver 110 comprises a relay group including an alarm relay R180, a start relay R185, a hold relay R190 and a timer relay R100. Finally, the alarm sender 100 comprises an alarm lamp L11|, a delayed alarm DA112 and a reset key K113.

In the main oflice 40, preferably each of the trunk circuits in the group, including the trunk circuit 800, is identical thereto; which trunk circut 800 terminates in the jack J8|5 before the operator switchboard 165, as previously noted and comprises a relay group including a sleeve relay R820, a signal-out relay R830, a jack relay R835, a hold relay R850, a dial relay R855, a signal-in relay R860, two re-ring relays R865 and R810, a switch relay R880 and an answer relay R890. Also, the trunk circuit 800 comprises a repeating coil RC815, as well as a busy lamp L8|1 disposed at the operator switchboard 165. At this point it is notedthat the trunk circuit 800 is connected to the carrier equipment 894 by a pair of line conductors C80| and C802, a signal-out conductor C803 and a signal-in conductor C804; and that the apparatus provided in the carrier equipment 894, as previously explained, comprises a signalin relay R895 and a signal-out relay R891.

In the main oliice 40, as shown in Fig. 8, preferably the local switch train 844, the toll switch train 805 and the incoming selectors 8|2, etc., are of the conventional Strowger types; while the distributor 843, the line circuits 842, etc., the CLR trunks 846, etc., and the toll trunks inward 809, etc., are of any suitable types. Finally, each of the subscriber substations T4| etc., is provided with conventional substation apparatus.

In the distant oidce 50, preferably each of the trunk -circuits is identical to the trunk circuit 900 which comprises, as shown in Figs. 9 and 10, a relay group including a signal-in relay R920, a hold relay R930, a. dial relay R940, a trouble relay R950, a seize relay R955, a switch relay R960, a re-ring relay R910 and an end-of-dial relay R980, an answer relay R915, a line relay R||0, a trouble relay R|020 and a re-ring relay R|025. Also, the trunk circuit 900 comprises a repeating coil RC9|0. At this point, it is noted that the trunk circuit 900 is connected to the carrier equipment 994 by a pair of line conductors C90| and C902, a signal-out conductor C903 and a signal-in conductor C904; and that the apparatus provided in the carrier equipment 994, as previously explained, comprises a signal-in relay R995 and a signal-out relay R991.

In the distant oiice 50, as shown in Fig. 10, preferably the local switch train |054, the toll switch train |038, the incoming selectors |036, etc., and the nder-selector links |062, etc., are of the conventional Strowger types; while the distributor |053, the line circuits |052, etc., the C. L. R. trunks |056, etc., and the toll trunks inward |066, etc., are of any suitable types. Further the Strowger dial toll board |060 is of the connection and arrangement of that disclosed in U. S. Patent No. 2,353,212, granted July 1l, 1944, to Harvey W. Balzer. Finally, each of the subscriber substations TSI, etc., is provided with conventional substation apparatus.

Local calls in the remote exchange 10 First assume that a call initiated at. a subscriber substation such, for example, as the subscriber substation T|| in the remote exchange I0 is to be extended to a paystation such, for example, as the paystation T|2 therein. When the call is initiated at the calling subscriber substation TI the line circuit 2 |3, associated with the subscriber line 2||, operates to mark the subscriber line 2|I as busy to the local connectors 205, etc., having access thereto, and to initiate operation of the distributor 204. The distributor 204 assigns an idle one of the lnder-selector links such, for example, as the finder-selector link 203 in the iirst group for use at this time; whereby the finder of the finder-selector links 203 operates to seize the subscriber line 2| The subscriber at the calling subscriber substation T|| then dials the directory number of the called paystation T|2, which may be 112. The selector of the lnder-selector link 203 responds to the rst digit 1 to select the rst group of local connectors, including the local connector 205, and then an idle local connector therein. For example, the selector of the finder-selector link 203 may select the trunk 201 extending to the particular local connector 205; whereupon the local connector 205 is rendered responsive to the next two digits dialed at the calling subscriber substation T||. The subscriber at the calling subscriber substation T|| then proceeds to dial the next two digits l and 2; whereby the local connector 205 is operated to seize the line 2 I2 extending to the called paystation T|2; whereupon the idle or busy condition of the line 2|2 is tested by the local connector 205 at this time. l

First assuming that the called paystation T|2 is busy at this time, the local connector 205 tests the line 2|2 extending thereto as busy returning busy tone current over the trunk 201, the linderselector link 203 and the subscriber line 2| to the calling subscriber substation T|| in order to indicate to the subscriber thereat that the desired connection may not be had at this time due to the busy condition of the called paystation T|2. The subscriber at the calling subscriber substation T|| then proceeds to release the apparatus in a manner more fully explained hereinafter.

Now assuming that the called paystation T|2 is idle at this time, the local connector 205 operates to project ringing current over the line 2|2 to the called paystation T| 2 and to return ring-back tone current over the trunk 201 and, consequently, to the calling subscriber substation T|| in order to indicate to the subscriber thereat that the called paystation T|2 is being rung. When a person at the called paystation T|2 answers the call, the local connector 205 operates in order to reverse the polarity of the trunk 201; whereby the finder-selector link 203 opertes the meter, not shown, associated with the subscriber line 2|| in order to meter the call in a conventional manner. At this time, an established connection is completed between the calling subscriber substation T| I and the called paystation T|2 and` conversation therebetween then proceeds in the usual manner.

At the conclusion of the established connection, when the person at the paystation TI2 disconnects, the local connector 205 again operates to reverse the polarity of the trunk 201; however, without eiect at this time. Subsequent1y, when the subscriber at the calling subscriber substation TII disconnects, the loop circuit extending to the local connector 205 is interrupted in order to cause the local connector 205 and the finderselector link 203 to be released. When the local connector 205 is thus released, the line 2I2 extending to the paystation TI 2 is again marked as idle by the associated line circuit 2 I4 to the 1ocal connectors 205, etc., having access thereto. Similarly, when the nder-selector link 203 is thus released, the line 2II extending to the subscriber substation TII is marked as idle by the associated line circuit 2 I 3 to the local connectors 205, etc., having access thereto. Also, when the finder-selector link 203 is thus released, the trunk 201 extending to the local connector 205 is marked as idle to the finder-selector links 203, etc., having access thereto. At this time the established connection between the calling subscriber substation TII and the called paystation TI2 is released and all of the apparatus involved therein is completely released and available for further use.

In view of the foregoing, it will be understood that a connection may be extended from a calling subscriber substation TI I, etc., in the remote exchange I to another called subscriber substation therein in an identical manner. Also, it will be understood that a connection from a calling paystation TI2, etc., in the remote exchange I0 may be extended to a called subscriber substation TI I, etc. or to another called paystation therein in a substantially identical manner. In this conjunction, it is noted incident to extending a connection from the calling paystation TI 2 in the remote exchange I0 to a called subscriber substation or to another called paystation therein, that when the call is answered, the local connector 205 operates to reverse the polarity of thetrunk 201 and over the finder-selector link employed and the line 2I2 to the calling paystation TI2. This reversal of polarity to the calling paystation TI2 brings about blocking of the transmitter at the calling paystation TI2 by the associated copper oxide rectier unless the person at the paystation TI2 has deposited a coin at this time. More particularly, in the event the person at the calling paystation TI2 has not deposited a coin at this time, he may hear the person at the called subscriber substation or at the called paystation in the remote exchange I0, but he may not talk to the person mentioned by virtue oi' the circumstance that the copper oxide rectifier blocks the associated transmitter as a conseouence of the reversal of polarity to the calling paystation TI 2. However, when the person at the calling paystation TI2 deposits a coin, the copper oxide rectier is removed from blocking the transmitter thereat; whereby the connection is completed in the manner previously explained.

First assume that a call initiated at a subscriber substation such, for example, as the subscriber substation TI I in the remote exchange I0 is to be extended to a subscriber substation such, for

16 example, as the subscriber substation T2I in the tandem exchange 20. When the call is initiated at the calling subscriber substation TI I, the line circuit 2I3 associated with the subscriber line 2II operates to mark the subscriber line 2II as busy to the local connectors 205, etc., having access thereto, and to initiate operation of the distributor 204. The distributor 204 assigns an idle one of the finder-selector links such, for examplejas the iinder-selector link 203 in the first group for use at this time; whereby the nder of the finder-selector link 203 operates to seize the subscriber line 2I I.

The subscriber at the calling subscriber substation TII in the remote exchange I0 then dials a prefix digit such, for example, as the prefix digit 9, indicating that the call is to be extended to the tandem exchange 20. followed by the directory number of the called subscriber substation T2I in the tandem exchange 20, which number may be 121. Thus the subscriber at the calling subscriber substation TII iirst dials the prex digit 9; whereby the selector of the finderselector link 203 responds to the first digit 9 in order to select the corresponding group of trunks, including the trunk 225, and then an idle trunk therein. For example, the selector of the linderselector link 203 may select the particular trunk 225, assuming that the trunk circuit 200 is idle at this time; the trunk 225 being marked as idle to the selector of the finder-selector link 203 by the application of battery potential to the control conductor C223 thereof. More particularly, battery potential is normally applied by way of the impedance 251, the contacts 266 and 383 to the control conductor C223 of the trunk 225.

Also, when the selector of the finder-selector link 203 seizes the trunk 225, a loop circuit is completed for energizing the upper and lower windings of the line relay R330 in the trunk circuit 200. This loop circuit extends from ground by way of the contacts 362, the lower winding of the line relay R330 and the contacts 244 to the line conductor C221 of the trunk 225; and from battery potential by way of the upper winding of the line relay R330 and the contacts 242 to the line conductor C220 of the trunk 225. When this loop circuit is thus completed, the line relay R330 operates to complete, at the contacts, 33|, an obvious circuit for operating the hold relay R380. Upon operating the hold relay R380 interrupts, at the contacts 383, a point in the previously traced path for applying battery potential to the control conductor C223 of the trunk 225; and completes, at the contacts 384, a path including the upper winding of the tone relay R390 for applying ground potential to the control conductor C223 of the trunk 225. When battery potential is thus removed from the control conductor C223 and ground potential is applied thereto, the trunk 225 and, consequently, the trunk circuit 200 is marked as busy to the selectors of the other finder-selector links having access thereto. Also the upper winding of the tone relay R390 is energized causing this relay to operate and complete, at the contacts 39|, an obvious path for applying ground potential to the tone start conductor C349, thereby to initiate operation of the associated tone apparatus. Also, the hold relay R380 interrupts, at the contacts 38|, a normally completed termination circuit also including the contacts 3II, the resistor 344, the contacts 28|, the condenser 288 and the condensers 341 and 348 across the line conductors C30I. and C302 extending to the carrier equipment 394. Also 

